I've answered a question on SO here. Embedded are two seemingly identical hyperlinks - but only one appears in markdown preview. Same when the page is returned from the server. The first was typed, the second pasted - after googling for the wikipedia page for 'Model-View-Controller'. Both links can be seen in the source.

@martin often the plain-ascii equivalent also works in wikipedia urls
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Jeff Atwood♦Sep 23 '10 at 7:54

interesting, time to update my Chrome and give it a spin. I was using Safari on OS X. Firefox escapes as does Chrome. I should have made the deductive leap from 'I see no differences' to 'the difference must be invisible'... Thanks again.
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martin claytonSep 23 '10 at 9:34

@Jeff - thanks - the ascii equivalent does indeed work here. Seems like Safari is somewhat lacking when it comes to copy-paste of URLs from the address bar with chars that need to be escaped.
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martin claytonSep 23 '10 at 22:18